Being the age of 18 or 19 does not mean you are an adult. I consider an adult someone who has a job, can pay for their own meals, and has their own place of residence. Basically, someone who can support him/herself.
I personally do not think that children should be getting pregnant. If they don't want to have a baby, they shouldn't have sex. Even if they are responsible and use sexual protection, there is a chance that the protection won't work. Also, getting pregnant at a young age is a danger to both the mother's and the child's health.